1. Field of the Invention
This invention relates to a magnetic disc cartridge, and more particularly to a magnetic disc cartridge comprising a thin shell and a magnetic disc which is formed integrally with a center core member and is supported for rotation in the shell.
2. Description of the Related Art
There has been known a magnetic disc cartridge which comprises a thin cartridge shell formed of a pair of shell halves of plastic mated together and a magnetic disc which is formed integrally with a center core member and is supported for rotation in the shell, the shell being provided with a magnetic head window through which a magnetic head of a recording and reproducing system is given access to the magnetic disc and a spindle hole through which a spindle of the recording and reproducing system is engaged with the center core member to rotate the magnetic disc with the center core member. The magnetic head window is provided with a shutter which closes the magnetic head window when the magnetic disc cartridge is not used in order to prevent dust and/or dirt from entering the cartridge.
A liner of nonwoven material is attached to the inner surface of the shell opposed to each side of the magnetic disc to prevent the surface of the magnetic disc from being damaged and to wipe dust and/or dirt off the surface of the disc when the disc is rotated.
Recently, with advent of a novel high density recording system, there has been developed a magnetic disc cartridge having a magnetic disc whose recording capacity is fifty times as large as that of the currently prevailing 3.5 inch floppy disc. In such a large capacity magnetic disc cartridge, the magnetic disc is rotated at much higher speed than the conventional magnetic disc cartridge in order to increase the recording density and the transfer rate and at the same time, the magnetic disc must be positioned with respect to the magnetic head at an extremely high accuracy.
In the large capacity magnetic disc cartridge, the magnetic disc is rotated at 2500 to 5000 rpm in order to ensure a high transfer rate. In such a case, wobbling of the surface of the magnetic disc occurs due to the condition of application of the center core member to the disc, curl of the disc itself and fluctuation in air flow between the inner surface of the shell and the surface of the disc.
Such wobbling of the disc surface is more apt to occur when the cross-section of the shell fluctuates across the shell due to unevenness on the inner surface of the shell.
Though the wobbling of the disc surface can be suppressed by a means which is brought into contact with the magnetic disc (e.g., by lifting the liner in the conventional micro floppy disc into contact with the disc), such an approach gives rise to a problem that frictional heat and/or damage on the disc are generated due to contact with the disc which is rotating at high speed.